The invention relates to a method for the operation of several adjacent ultrasonic sensors which are synchronized. A first ultrasonic sensor emits first transmission pulses, a second ultrasonic sensor emits second transmission pulses, and a third ultrasonic sensor emits third transmission pulses.
A method of this type is described in European Patent Application EP 0 519 090 B1. In the operation of adjacent ultrasonic sensors, mutual influence can occur as a result of unfavorable reflections of the ultrasound in the area of the ultrasonic sensors. If the ultrasonic sensors do not transmit synchronously, the run-time measurement of an ultrasonic sensor is disturbed by the echo signal of the adjacent ultrasonic sensors. It is then possible that the echo signals will not be correctly assigned to the ultrasonic sensors which have emitted the corresponding transmission pulses. Therefore, errors occur in the run-time evaluation because the switching output is undefined. To solve this problem, it has been known in the past to operate the ultrasonic sensors serially so that the supply voltages of the ultrasonic sensors are cyclically switched on or off. The response time of the ultrasonic sensors in this technique is correspondingly lengthy. Additionally, the response time is further delayed through internal reset times. Another possibility for avoiding mutual influence, in the past, has included complying with mounting instructions, i.e., by specifying minimum distances for the installation of the ultrasonic sensors. The minimum distances, however, are very dependent on the respective application. For many potential applications, this method is not suitable, if a high degree of reliability is required. An additional solution for avoiding mutual influence includes connecting the adjacently operated ultrasonic sensors to each other through a common conductor via their release output. Through this arrangement, a parallel synchronization takes place. In this case, transmission pulses are emitted by all proximity switches at the same point in time so that the problem of correct temporal assignment of the echo signals to the appropriate ultrasonic sensors is avoided. Parallel synchronization of this type, however, has the drawback that the run-time evaluation does not contain a systematic evaluation algorithm. European Patent Application EP 0 519 090 B1 describes the connection of several ultrasonic sensors via their release outputs through a common conductor with automatic parallel or serial synchronization.
However, the sampling of rapid events, as is required, for example, for counting automobiles in the entrance to a parking garage, represents a problem which has not yet been solved.